Development of a Torque Sensor using Giant Magnetostrictive Material for Electric Power-Assisted Bicycles

Abstract

We developed a new light-weight power-assisted bicycle using a giant magnetostrictive torque sensor, which is a new mechatronics product for individual use. The key components for power-assisted bicycles are sensors, which are vital for detecting the extremely large forces (maximum crank axle torque: about 160Nm) of power exerted on the pedals by the riders. In this paper we propose a torque detection method that uses a giant magnetostrictive material with a high force detection sensitivity, where the capacity to resist stress is extremely large.Improving the hysteresis has become an issue for raising the precision of force sensors that use giant magnetostrictive elements. As a method to improve the hysteresis, we focus on the point of integrating these force sensors into microcomputer-equipped digital control systems, and construct a detection circuit such that the magnetostrictive elements are expanded instantaneously by the application of a pulse magnetic field during the sampling of discrete sensor data. this paper also examines this hysteresis reduction method and reports the contents of an actual construction method for force sensors.